Multi-conductor communication cables are currently insulated with plastic but still are not waterproof. Water can enter the cable jacket and destroy the cables usefulness. There have been many attempts at building barriers to such leakage of water. The remedy currently adapted to combat this problem has been to fill the voids between the conductors with a water repellant substance. Further, with the necessity to use loading coils in the cable it is also necessary to protect the loading coil. These are commonly grouped in a case with a cable stub that must be spliced onto the cable. This cable stub, however, must remain workable until after installation and therefore cannot be filled prior to installation, while it is preferable that the coils be sealed at the manufacturing site. This therefore requires a dam within the cable at the interface with the loading coil package.
Polyurethane of low viscosity is the desired filler for the loading coil assembly, but it penetrates to an excessive depth into the cable. This then makes the cable difficult to handle at the time of installation due to its rigidity. Numerous processes were used at various times in the past and some are still in use. However, all of the processes leave much to be desired and all are very labor intensive.
Examples of some of these processes are the use of small quantities of the potting material being applied and allowing adequate time to jell between applications; band clamps to restrict the diameter of the cable; internal plugs inserted to make a desired area in the cable more dense and thus impede the flow of the polyurethane beyond the desired point; and fast setting polyurethane among others.